I'm a little late in continuing with this report on the Ostrom Smposium,
but I hope that I may still have a few interesting things to add after the
reports that have been published by other people on this list.
In the course of going over my notes, I discovered that I had accidentally
missed a few pages of jottings on some of the papers from the first day,
from about the middle of Luis Chiappe's paper to the discussion. So my
apologies, and back to the middle of Chiappe's paper, and some interesting
conclusions about the enantiornithes. Chiappe does not believe that there
is a group called "Saururae" that includes both the enantiornithes and
earlier toothed birds including Archaeopteryx. He pointed out a number of
differences between enantiornithine birds and earlier forms, including a
much shorter first digit (the first digit of Confuciusornis, for example,
is very long, longer than metatarsal two).
Chiappe examined the three characters given as support for Saururae: the
structure of the furcula, the ischium, and the fusion of the metatarsae.
Though broad furcular arms are given as a character for Saururae, the
furcula of Archaeopteryx is boomerang-like, while that in the
enantiornithes is a very different V shape. The anterodorsal ischial
process does unite these taxa, but it is also found in more primitive forms
such as Unenlagia and in Rahonavis. The same is true of proximodistal
metatarsal fusion, which is another primitive character. The advantage
Chiappe puts forward for his own tree, with a clade Pygostylia uniting
enantiornithines and modern birds, is that it only requires a single
evolution of advanced flight characteristics including a keeled sternum,
alula, pygostyle, and strut-like coracoids. Accepting Saururae as a taxon
would require that these characters arose twice, once in the
enantiornithine line and once in modern birds. Chiappe, in short,
concludes that "Saururae" is clearly paraphyletic.
We then moved on, after lunch, to a series of papers on the relationships
of modern birds, something that was (as some other people have pointed out)
ostensibly a little more in my line than the more dinosaurian papers we had
been hearing so far. The first of these was given by Joel Cracraft, an old
fellow graduate student of mine. However, though I will confess to some
knowledge of birds, my knowledge of molecular genetics is far less
terrific. I am not sure that I can really comment on a methodology that
dismisses DNA-DNA hybridization, which used to be about as cutting edge as
you can get, as old hat compared to gene sequencing.
For those of you who are not familiar with the debate, DNA-DNA
hybridization was used by the late Dr. Charles Sibley and John Ahlquist to
completely revise our traditional understanding of the way that modern bird
orders ought to be arranged. Their classification has never quite replaced
the traditional one, certainly in popular bird books at least, but it has
at the very least aroused a lot of discussion and, in my view, has some
intellectually satisfying aspects to it. Joel criticized the tree that
Sibley and Ahlquist developed, but his own tree had some resemblance is too
their conclusions (with, admittedly, a nod or two to traditional
arrangements). For example, Joel agrees that the ratites form a sister
group to all other living birds, and also supports the idea that ducks and
their relatives, clustered together with chickens and pheasants and their
relatives, form a clade called Galloanserae. On the other hand, Joel does
not agree that the Piciformes are polyphyletic (this is the group that
traditionally unites woodpeckers with various tropical birds such as
barbets, toucans, jacamars and puffbirds) and and restores them to their
close association with the largest importer of birds, the pass era for maze
or perch in birds. And he also own tree be Luis and ingredients, the two
most highly modified living quarters of guiding birds, as to each other's
closest relatives, a conclusion that, I would say, few ornithologists
share. Although he seems to support Sibley's association of a large number
of water birds with each other, he admits that the relationships within
this assemblage are "confusing". Joel emphasized that is conclusions were
not final, and that he had difficulties in understanding of what was going
on when the morphological and molecular data failed to produce the same
result. Possibly, he said, this was the result of improper coding of
morphological characters, or insufficient sampling, or, perhaps, a lot of
homoplasy at the molecular level.
Jeff Groth then describe his study of the phylogeny of living birds using
nuclear DNA sequencing. Although his study was only based on 16 taxa, he
claimed one advantage over Sibley's work -- the use of an outgroup, in this
case a crocodilian. The same outgroup was used in a study of mitochondrial
DNA published by Mindell and others in 1997. Nuclear DNA, according to
Groth, may be evolving much more slowly that mitochondrial DNA, at least at
lower divergence levels (mitochondrial DNA apparently reaches a "plateau"
of divergence, though I haven't the faintest idea why.)
I found two of Groth's conclusions particularly interesting. One was that
his tests do not support a molecular clock. If this is correct I assume
that the claims that the orders of living birds must have diverged much
earlier than the fossil evidence would suggest may be incorrect, something
that would certainly not bother me. His most interesting finding, as far
as I was concerned, was the synapomorphic deletion of a sequence in one of
the genes he examined, shared by all birds except ratites and
Galloanserae, a finding that supports the view that the ratites are a
sister group of other living birds and, among those birds, the Galloanserae
are a sister group to the remainder.
Bradley Livezey then described his morphological studies on basal
Neognathae. Livezey's work also supports the concept of the Galloanserae,
though he admitted that it is hard to assess skull features in birds for
phylogenetic purposes, because of the extensive fusion of the bones of the
skull, which makes it very difficult to determine where elements end and
others begin.
After these three papers, you might be forgiven for thinking that the
reality of the Galloanserae was a settled matter. Therefore the title of
Per Ericson's paper, "Higher level systematics in living birds: or is
Galloanserae fact or fiction?" might seem rather strange. But Ericson's
morphological data set, even when combined with the data from Livezey's
study, does not support the Galloanserae as a monophyletic group.
Molecular data does support the group, but the tree that results is
unresolved. Ericson believes that the problem of whether there really is
such a clade is not settled.
One thing that Livezey and Ericson to agree on is the position of
Presbyornis, a long-legged duck-like fossil that Alan Feduccia and Storrs
Olson have claimed as a link between ducks and shorebirds. However, this
fossil appears to be a perfectly good sister group to the Anatidae, the
family that includes all living ducks and geese (and the whistling ducks,
sometimes given separate family status) except for the Australian Magpie
Goose which is put in its own family, Anseranatidae. In both studies, if I
recall correctly, the Magpie Goose forms a sister group to Presbyornis plus
Anatidae.
Ericson then turned to the vexing question of what a primitive neornithine
bird would be like. Presbyornis, shorebirds, the Magpie Goose, screamers,
and fossil taxa such as Juncitarsus and the graculavids, share a number of
characters that are presumably plesiomorphic. Only a single early
representative of the Galliformes (chicken-like birds) is known,
Gallinuloides, which is similar to the modern cracids. The shoulder girdle
and sternum of these birds is, however, unlike that in ducks and
shorebirds, leaving open the question of whether the plesiomorphic
characters in ducks are primitive within the Neognathae, or only within a
subgroup including ducks and shorebirds.
Ericson finished with a few really surprising suggestions. Noting that
Larry Martin has suggested that neornithine birds involved in shore
environments, in contrast to the enantiornithines, he suggested that
Ichthyornis might be an example of a basal neornithine, teeth and all.
More skeletal work on this bird is sorely needed. For me, even more
astonishing was the suggestion, based on a study of mitochondrial DNA, that
the Passeriformes (songbirds or perching birds) represent the most basal
neornithine lineage. The Passeriformes have almost always been regarded as
not only a highly derived group, but the most recent bird order to evolve.
In the northern hemisphere, they are pretty much unknown before the
Miocene. However, Walter Boles of the Australian Museum, who was at the
conference, has describe Australian material that seems to represent a far
older representative of the order. In fact, Ericson put forward the
surprising idea that the Passeriformes and the Galliformes together are a
sister group of the tinamous, the only flying birds within the ratites.
Needless to say, this startling conclusion will need some verification.
That completes the birds papers from the first day. On the second day we
got back to the Mesozoic, feathers and all. Stay tuned!
--
Ronald I. Orenstein Phone: (905) 820-7886
International Wildlife Coalition Fax/Modem: (905) 569-0116
1825 Shady Creek Court
Mississauga, Ontario, Canada L5L 3W2 mailto:ornstn@home.com